Hierarchical Compliance Control of a Soft Ankle Rehabilitation Robot Actuated by Pneumatic Muscles

Traditional compliance control of a rehabilitation robot is implemented in task space by using impedance or admittance control algorithms. The soft robot actuated by pneumatic muscle actuators (PMAs) is becoming prominent for patients as it enables the compliance being adjusted in each active link, which, however, has not been reported in the literature. This paper proposes a new compliance control method of a soft ankle rehabilitation robot that is driven by four PMAs configured in parallel to enable three degrees of freedom movement of the ankle joint. A new hierarchical compliance control structure, including a low-level compliance adjustment controller in joint space and a high-level admittance controller in task space, is designed. An adaptive compliance control paradigm is further developed by taking into account patient’s active contribution and movement ability during a previous period of time, in order to provide robot assistance only when it is necessarily required. Experiments on healthy and impaired human subjects were conducted to verify the adaptive hierarchical compliance control scheme. The results show that the robot hierarchical compliance can be online adjusted according to the participant’s assessment. The robot reduces its assistance output when participants contribute more and vice versa, thus providing a potentially feasible solution to the patient-in-loop cooperative training strateg

Robust iterative feedback tuning control of a compliant rehabilitation robot for repetitive ankle training

Robot-assisted rehabilitation offers benefits, such as repetitive, intensive, and task-specific training, as compared to traditional manual manipulation performed by physiotherapists. In this paper, a robust iterative feedback tuning (IFT) technique for repetitive training control of a compliant parallel ankle rehabilitation robot is presented. The robot employs four parallel intrinsically compliant pneumatic muscle actuators that mimic skeletal muscles for ankle's motion training. A multiple degrees-of-freedom normalized IFT technique is proposed to increase the controller robustness by obtaining an optimal value for the weighting factor and offering a method with learning capacity to achieve an optimum of the controller parameters. Experiments with human participants were conducted to investigate the robustness as well as to validate the performance of the proposed IFT technique. Results show that the normalized IFT scheme will achieve a better and better tracking performance during the robot repetitive control and provides more robustness to the system by adapting to various situations in robotic rehabilitation

Collaborative system and multi robots based on pneumatic muscle actuator

Designing a multi-robot system provides numerous advantages for many applications, such as low cost, multi-tasking and more efficient group work. While the rigidity of the robots used in industrial and medical application increase the probability of risk of injury. Therefore, many researches are done to increase the safety factor for robot-human interaction, as a result, either the separated between the human and robot is suggested or the force shutdown to robot system is applied. These solutions might be useful for industrial applications, nonetheless it is not for medical and the application require the direct interaction between the human and machine. To overcome the rigidity problem, a soft pneumatic muscle actuator PMA is used in this thesis to design a fully soft robot arm.The performances and the behaviours of these actuators are tested to enhance the force formula for the contraction and the extension PMAs. General length formulas are proposed in terms of the initial length in addition to the structure-based formulas for the tensile force and length. Three different novel actuators are proposed together with their kinematics. These actuators include: the self-bending contraction actuator SBCA, the double-bend pneumatic muscle actuator DB-PMA and the circular pneumatic muscle actuator CPMA. The presented actuators are used with the simple contraction and extension actuators to design different novel structures of continuum arms and end effectors. Then an efficient control system is proposed by using a parallel structure of the neural network NN and proportional P controller (PNNP controller). The presented continuum arms formed a multiple robot system to perform several tasks under the PNNP controller

Design and implementation of a novel lightweight soft upper limb exoskeleton using pneumatic actuator muscles

Stroke is the leading cause of disability and weakness in the UK and around the world. Thus, stroke patients require an extensive rehabilitation therapy to regain some of the weaknesses. Many rehabilitation robotic devices have been designed and developed to assist the stroke patients to perform their activities of daily living and to perform repetitive movements. However, these devices remain unmanageable to use by the patients alone not only because they are cumbersome to use but also due to their weights, rigid, fix and non-portable characteristics. Thus there is a need to invent a novel exoskeleton soft arm that has a lightweight and a high power to rehab the elbow joint with lower cost and without the need to therapists. Here for elbow joint rehabilitation, we investigate and propose a novel exoskeleton soft robotic arm, which is wearable, lightweight and portable so that it would allow patients to perform repetitive motion therapy more often with a greater intensity in their homes and relevant to their Activities of Daily Living (ADL). The proposed arm consists of various bending pneumatic muscle actuators (pMA), where traditional pMA are not suitable. Testing on various pMA (traditional and bending) revealed its behaviour and the relationship between pressure, length, force, and bending angle in different setups such as isotonic and isometric. Experiments are done to analyse its non-linear behaviour, moreover, geometrical and numerical models are compared to the experimental results to validate the results. A developed control approach to control the soft arm is implemented to validate the design. Model reference adaptive control (MRAC) to control the arm using (Proportional, Integral, and Derivative) PID controller as an input for MRAC. Neural Network (NN) is also used in MRAC to improve the performance of MRAC

Modeling and control of a pneumatic muscle actuator

This thesis presents the theoretical and experimental study of pneumatic servo position control systems based on pneumatic muscle actuators (PMAs). Pneumatic muscle is a novel type of actuator which has been developed to address the control and compliance issues of conventional cylindrical actuators. Compared to industrial pneumatic cylinders, muscle actuators have many ideal properties for robotic applications providing an interesting alternative for many advanced applications. However, the disadvantage is that muscle actuators are highly nonlinear making accurate control a real challenge. Traditionally, servo-pneumatic systems use relatively expensive servo or proportional valve for controlling the mass flow rate of the actuator. This has inspired the research of using on/off valves instead of servo valves providing a low-cost option for servo-pneumatic systems. A pulse width modulation (PWM) technique, where the mass flow is provided in discrete packets of air, enables the use of similar control approaches as with servo valves. Although, the on/off valve based servo-pneumatics has shown its potential, it still lacks of analytical methods for control design and system analysis. In addition, the literature still lacks of studies where the performance characteristics of on/off valve controlled pneumatic systems are clearly compared with servo valve approaches. The focus of this thesis has been on modeling and control of the pneumatic muscle actuator with PWM on/off valves. First, the modeling of pneumatic muscle actuator system controlled by a single on/off valve is presented. The majority of the effort focused on the modeling of muscle actuator nonlinear force characteristics and valve mass flow rate modeling. A novel force model was developed and valve flow model for both simulation and control design were identified and presented. The derived system models (linear and nonlinear), were used for both control design and utilized also in simulation based system analysis. Due to highly nonlinear characteristics and uncertainties of the system, a sliding mode control (SMC) was chosen for a control law. SMC strategy has been proven to be an efficient and robust control strategy for highly nonlinear pneumatic actuator applications. Different variations of sliding mode control, SMC with linear model (SMCL) and nonlinear model (SMCNL) as well as SMC with integral sliding surface (SMCI) were compared with a traditional proportional plus velocity plus acceleration control with feed-forward (PVA+FF) compensation. Also, the effects of PWM frequency on the system performance were studied. Different valve configurations, single 3/2, dual 2/2, and servo valve, for controlling a single muscle actuator system were studied. System models for each case were formulated in a manner to have a direct comparison of the configuration and enabling the use of same sliding mode control design. The analysis of performance included the sinusoidal tracking precision and robustness to parameter variations and external disturbances. In a similar manner, a comparison of muscle actuators in an opposing pair configuration controlled by four 2/2 valves and servo valve was executed. Finally, a comparison of a position servo realized with pneumatic muscle actuators to the one realized with traditional cylinder was presented. In these cases, servo valve with SMC and SMCI were used to control the systems. The analysis of performance included steady-state error in point-to-point positioning, the RMSE of sinusoidal tracking precision, and robustness to parameter variations

Modeling and control of a pneumatic muscle actuator

This thesis presents the theoretical and experimental study of pneumatic servo position control systems based on pneumatic muscle actuators (PMAs). Pneumatic muscle is a novel type of actuator which has been developed to address the control and compliance issues of conventional cylindrical actuators. Compared to industrial pneumatic cylinders, muscle actuators have many ideal properties for robotic applications providing an interesting alternative for many advanced applications. However, the disadvantage is that muscle actuators are highly nonlinear making accurate control a real challenge. Traditionally, servo-pneumatic systems use relatively expensive servo or proportional valve for controlling the mass flow rate of the actuator. This has inspired the research of using on/off valves instead of servo valves providing a low-cost option for servo-pneumatic systems. A pulse width modulation (PWM) technique, where the mass flow is provided in discrete packets of air, enables the use of similar control approaches as with servo valves. Although, the on/off valve based servo-pneumatics has shown its potential, it still lacks of analytical methods for control design and system analysis. In addition, the literature still lacks of studies where the performance characteristics of on/off valve controlled pneumatic systems are clearly compared with servo valve approaches. The focus of this thesis has been on modeling and control of the pneumatic muscle actuator with PWM on/off valves. First, the modeling of pneumatic muscle actuator system controlled by a single on/off valve is presented. The majority of the effort focused on the modeling of muscle actuator nonlinear force characteristics and valve mass flow rate modeling. A novel force model was developed and valve flow model for both simulation and control design were identified and presented. The derived system models (linear and nonlinear), were used for both control design and utilized also in simulation based system analysis. Due to highly nonlinear characteristics and uncertainties of the system, a sliding mode control (SMC) was chosen for a control law. SMC strategy has been proven to be an efficient and robust control strategy for highly nonlinear pneumatic actuator applications. Different variations of sliding mode control, SMC with linear model (SMCL) and nonlinear model (SMCNL) as well as SMC with integral sliding surface (SMCI) were compared with a traditional proportional plus velocity plus acceleration control with feed-forward (PVA+FF) compensation. Also, the effects of PWM frequency on the system performance were studied. Different valve configurations, single 3/2, dual 2/2, and servo valve, for controlling a single muscle actuator system were studied. System models for each case were formulated in a manner to have a direct comparison of the configuration and enabling the use of same sliding mode control design. The analysis of performance included the sinusoidal tracking precision and robustness to parameter variations and external disturbances. In a similar manner, a comparison of muscle actuators in an opposing pair configuration controlled by four 2/2 valves and servo valve was executed. Finally, a comparison of a position servo realized with pneumatic muscle actuators to the one realized with traditional cylinder was presented. In these cases, servo valve with SMC and SMCI were used to control the systems. The analysis of performance included steady-state error in point-to-point positioning, the RMSE of sinusoidal tracking precision, and robustness to parameter variations

Design and Evaluation of AIRGAIT Exoskeleton\u27s Leg Orthosis: Development of a Control Scheme and Strategy for a Noble Control of Antagonistic Mono- and Bi-Articular Actuators

芝浦工業大学201